1. Field of the Invention
The present invention relates to a magneto-resistance effect element, and a magnetic head and magnetic read apparatus both of which use that element.
2. Description of the Related Art
In a magnetic recording apparatus such as a HDD, to improve recording density, narrowing of a recording track width of a read medium is under way. To compensate decrease of read output power accompanying this narrowing of a recording track width, demand for a magnetic head provided with a high sensitive magneto-resistance effect element (MR element) is becoming large. In particular, an MR head possessing a spin valve film consisting of a magnetic multi-layered film having a ferromagnetic layer of which magnetization rotates according to a signal magnetic field (hereinafter refer to as a free layer), a non-magnetic layer, a ferromagnetic layer of which magnetization is pinned (hereinafter referred to as a pinned layer), and an antiferromagnetic layer for pinning the magnetization of the pinned layer, and showing a giant magneto-resistance effect is seen as a potential candidate.
In an MR head using a spin valve film, Barkhausen noise caused by discontinuous movement of Bloch wall of a free layer is a big problem in putting to practical use. To circumvent such a problem, an MR head of a so-called abutted junction structure is proposed, wherein, as shown in FIG. 44, outsides of both edge portions off a recording track width W.sub.t of a spin valve film 1 are etched away to eliminate and thereon hard magnetic layers 2 are respectively disposed as hard magnetic biasing films.
As another MR head, as shown in FIG. 45, a so-called overlaid structure is proposed as a bias magnetic field inputting film, wherein, on a pair of hard magnetic layers 2, outside portions of the both edge portions of a spin valve film 1 are at least stacked. A pair of hard magnetic layers 2 are disposed in advance in a region off a recording track width W.sub.t of a spin valve film 1.
In an MR head in which the above described bias structure is applied, by removing Bloch wall of the free layer 3 with a bias magnetic field from a hard magnetic layer 2, occurrence of Barkhausen noise is suppressed. Here, in each spin valve MR head shown in FIG. 44 and FIG. 45, a spin valve film 1 is fundamentally consisting of a free layer 3, a non-magnetic layer 4, a pinned layer 5, and an antiferromagnetic layer 6. On a hard magnetic layer 2 (FIG. 44) or on a spin valve film 1 (FIG. 45), a pair of electrodes 7 for supplying a sense current to a spin valve film 1 are formed.
A spin valve film 1 is interposed between a pair of upper and lower magnetic shield layers 9a, 9b disposed respectively through a magnetic gap films 8a, 8b. These constitute a shield type MR head. In addition, for enhancing sensitivity of a spin valve film 1, as a constituent material of a free layer 3 and a pinned layer 5, a ferromagnetic material containing Co such as a CoFe alloy is effective.
Now, to respond to further high densification of magnetic recording density, even in a spin valve MR head, further gap narrowing (thinning of magnetic gap films 8a, 8b) is being demanded. When the above described bias structure is applied in such a narrow gapped MR head, there is a problem that effective bias power can not be obtained. That is, even if it is tried to enhance the bias force by increasing a film thickness of a hard magnetic layer 2 as a hard magnetic biasing film, since the bias magnetic field leaks to the magnetic shield layers 9a, 9b, effective bias force can not be obtained.
Further, recently, to attain stabilization of a pinned layer or improvement of off-track characteristics thereof, a spin valve film of a reversed structure in which positions of a free layer 3 and a pinned layer 5 are reversed is proposed. In a spin valve film of a reversed structure, antiferromagnetic layer/pinned layer/non-magnetic layer/free layer are stacked in turn from a substrate side. Further, to attain high sensitivity of an MR head, a dual element spin valve film having 2 of free layer or pinned layer is proposed. In the MR heads using these spin valve films, it is becoming particularly difficult to input effectively a bias magnetic field to a free layer.
Besides, concerning a structure of a spin valve film, a hard magnetic film is proposed to be applied in a pinned layer. However, a spin valve film using a conventional hard magnetic film, since magnetization directions of the hard magnetic film are not aligned to the film plane, there is a problem that influence of ferromagnetic coupling through a non-magnetic layer becomes large. If the influence of the ferromagnetic coupling becomes large, it adversely affect on magnetization behavior of a free layer.
A spin valve film is also being investigated to use as a magneto-resistance effect memory such as an MRAM, for example. A hard magnetic film is being studied to be used as a ferromagnetic layer in which information of such a magneto-resistance effect memory is memorized. However, a conventional hard magnetic film has caused performance deterioration as a spin valve film.
As described above, in an MR element using a spin valve film, an abutted junction structure or an overlaid structure employing a hard magnetic biasing film is fundamentally effective in suppression of Barkhausen noise due to domain wall of a free layer. However, by narrowing a gap or a track of an MR head, it is becoming difficult to effectively input a bias magnetic field to a free layer.
In particular, in an MR head in which a spin valve film of a reversed structure or a spin valve film of a dual element type structure is employed, since a position of the free layer is different from the conventional spin valve film, it is difficult, in a conventional bias structure, to input effectively a bias magnetic field.
Further, in a conventional spin valve film in which a hard magnetic film is used as a constituent element, since magnetization directions of the hard magnetic film are not aligned to the film plane, there is a problem that it is difficult to obtain characteristics capable of being putted to practical use as an MR head or an MRAM.